ONE-PHOTON AND 2-PHOTON PUMP-PROBE SPECTROSCOPY OF PHOTOACTIVE YELLOWPROTEIN

We present the results of nonlinear optical pump-probe experiments on photoactive yellow protein (PYP). We are able to completely bleach the 446 nm absorption peak of PYP by one-photon excitation using a cw arg on laser. We calculate the corresponding index change and find it to b e similar to that of bacteriorhodopsin. We also determine an upper lim it to the two photon absorption cross-section of PYP by looking for bl eaching of the 446 nm absorption peak under irradiation by femtosecond pulses at 820-910 nm. No TPA signal is observed.